Flame retardant polyester compositions

ABSTRACT

LINEAR SATURATED POLYESTERS AND PARTICULARLY POLY(ETHYELENE TEREPHTHALATE) WITH IMPROVED FLAME RETARDANCY ARE PROVIDED WHICH CONTAIN FROM 3 TO 15% OF A HOMOPOLYETHER OR COPOLYMER OF AN OXETANE SUBSITUTED IN THE THREE POSITION BY 1 OR 2 BROMOMETHYL GROUPS OR WITH FROM 1 TO 15% OF SAID POLYETHER AND FROM 0.5 TO 5% OF AN ANTIMONY COMPOUND.

United States Patent US. Cl. 26040 R 6 Claims ABSTRACT OF THE DISCLOSURE Linear saturated polyesters and particularly poly(ethylene terephthalate) with improved flame retardancy are provided which contain from 3 to 15% of a homopolyether or copolymer of an oxetane substituted in the three position by 1 or 2 bromomethyl groups or with from. 1 to 15% of said polyether and from 0.5 to of an antimony compound.

This invention relates to improving the flame retardancy of polyesters without major impairment of the physical and mechanical properties of the polyester and to the improved flame retardant compositions produced thereby.

It is known that the flame retardancy of thermoplastics can be improved by the incorporation of halogen compounds, and particularly chlorinated hydrocarbons therein. Relatively large amounts of the chlorined hydrocarbon and an inorganic flame retardant such as antimony trioxide, however, are required to produce an acceptable flame resistant product.

It is also known that certain bromine compounds are more effective flameproofing agents than the corresponding chlorine compounds, and that flame retardancy can be achieved with much smaller amounts of additives. Most bromine-containing compounds, however, are not stable at the elevated temperatures required for molding or spinning into fibers such polyesters as poly(ethylene terephthalate) and the like.

It is an object of the present invention to provide flame retardant linear saturated polyester compositions using particularly small amounts of flame retardant additives. Another object is to provide compositions which can be molded into flame retardant articles without major impairment of the mechanical and physical properties.

Now in accordance with the present invention it has been found that the aforesaid objects can be achieved through the use of linear saturated polyester compositions which contain as a flame retardant, based on the weight of the composition, from 3 to 15% and preferably from 3 to of a bromine-containing polyether when the polyether is the sole flame retardant or from 1 to and preferably from 1 to 10% of said polyether combined with from 0.5% to 5% of an antimony compound, said polyether having a bromine content of at least 48% and being a polymer of R3 R JH R2 where R is a bromine substituted methyl group, R is R, chloromethyl, alkoxymethyl or an alkyl group, and R and R are hydrogen or an alkyl group.

In the above formula R, as stated is a bromine substi tuted methyl group and can be CH Br, CHBr or -CBr R in addition to being chloromethyl, alkoxymethyl or alkyl can also be a bromine substituted methyl group, i.e., a CH Br, -CHBr or CBr group and can be the same as or difference from the R substituent.

3,645,962 Patented Feb. 29, 1972 Suitable alkyl groups which R R and R can be will generally contain from 1 to 18 carbon atoms and typically from 1 to 6 carbon atoms. Particularly preferred alkyl groups are methyl, and ethyl groups. Likewise the alkoxy group of the alkoxymethyl substituents which R can comprise will usually contain from 1 to 18 carbon atoms and preferably from 1 to 6 carbon atoms. Ethoxymethyl substituents are particularly preferred.

Thus the invention provides flame retardant compositions from polyesters with very little or no antimony compound, and relatively low amounts of the bromine-containing polyether. Moreover, because of the small amount of flame retardant constituents required; the physical and mechanical properties of the compositions are not impaired to any appreciable extent. The compositions of the invention are suitable for the production of molded articles by the usual processing methods and are particularly suitable for the production of film, fiber and plastic molded articles. Additionally, because the brominecontaining polyether is thermally stable at conventional molding or extrusion temperatures, problems of discoloration and voiding in molded articles, mold corrosion, or loss of additives during processing are not encountered.

The polyethers useful in the present invention contain at least 48% bromine and preferably from 60 to 70% bromine and are homopolymers of an oxetane containing one or two bromine-substituted-methyl groups in the 3-position or copolymers thereof with up to about 50 molar percent of a different epoxide which can be an oxirane or oxetane. Monomers that can be copolymerized with the above mentioned oxetane include the alkylene oxides such as ethylene oxide, propylene oxide, l-butene oxide, cis and trans Z-butene oxides, isobutylene oxide, l-hexene oxide; the substituted alkylene oxides such as cyclohexene oxide, epoxycyclooctene, styrene oxide; the alkyl glycidyl ethers such as methyl glycidyl ether, ethyl glycidyl ether, methylethyl glycidyl ether and butyl glycidyl ether; glycidyl ethers of phenol, bis-phenol and the like; unsaturated epoxides such as vinyl cyclohexene monoand di-oxides, butadiene monoxides, allyl glycidyl ether, allyl phenyl glycidyl ether and crotyl phenyl glycidyl ether; halogen containing epoxides such as epichlorohydrin, epibrornohydrin, epifluorohydrin, perfluoropropylene oxide, perfluoroethylene oxide; the cis and trans l,4-dihalo-2,3-epoxy-butanes; the 1,1,1-trihalo- 3,4-epoxy butanes; and a different oxetane which can be oxacyclobutane itself, oxacyclobutane carrying on one or more of the carbon atoms substituents such as halo gen, cyanide, hydroxyl, alkoxy, acyloxy, aryloxy, halomethyl, cyanomethyl, hyd-roxymethyl, alkoxymethyl, acyloxymethyl, aryloxymethyl and the like. Typical polyethers that can be used are those described in US. 3,205,- 207 and 3,341,475.

The polyethers of the invention will have a weight average molecular weight of at least about 700 and preferably of the order of about 3000 and higher. The polyethers can be prepared in known manner, as by polymerizing the bromo-substituted oxetane' or mixtures thereof with a different epoxide using a Friedel-Crafts catalyst or by the procedure described in US. 3,205,183.

The polyesters which can be made flame retardant in accordance with this invention are the thermoplastic resins which are the linear, saturated polyesters of aromatic dicarboxylic acids and saturated diols and preferably the polyester of terephthalic acid and ethylene glycol. The polyesters are obtained by known methods from aromatic dicarboxylic acids, preferably terephthalic acid and the lower alkyl esters thereof such as the dimethyl ester of terephthalic acid. The aromatic dicarboxylic acid or its ester is esterified or transesterifled and polycondensed with a saturated diol such as ethylene glycol, the resulting polycondensate having an average molecular weight of at least about 10,000, corresponding to an intrinsic viscosity of at least about 0.4 measured as a 1% solution in 60/40 phenol/tetrachloroethane at 25 C. The saturated diols ated according to the horizontal burning test ASTM D635, samples will pass the test regardless of whether or not a flame retardant additive is present because the ignited end melts and drops from the test specimen, thus pre are saturated aliphatic, cycloaliphatic or aromatic diols, 5 maturely removing the ignition front and leading to deceppreferably the lower alkane diols such as ethylene glycol. tive results. Likewise, in the measurement of combustion Mixtures of acids or saturated diols can also be used. Howindex according to the method of C. P. Fenimore and F. ever, it is preferably the lower alkane diols such as ethyl- C. Martin, Combustion and Flame, 10, 135 (196-6) meltene glycol. Mixtures of acids or saturated diols can also ing of the polyester removes heat from the surface of the be used. However, it is preferred to employ a polyester specimen and leads to unrealistically high results which consisting essentially of poly(ethylene terephthalate), i.e., do not accurately reflect the contribution of any flame rewherein not more than 10 molar percent, preferably less tardant additive present. A similar phenomenon also than 5 molar percent of the monomeric components are occurs in the evaluation of flammability according to the derived from sources other than terephthalic acid and vertical burning test -UL746 (Standards for Thermoplastic ethylene glycol. The preferred poly(ethylene terephthal- 1 Insulated Wires, 3rd edition, 17, 1948). However, by ate)s,usually have a molecular weight of at least about modifying test (11.746 with respect to the size of the 1 6,000 and an intrinsic viscosity of at least about 0.5. sample, height of flame and time of flame contact in order The polyesters, and particularly those for molding to moderate the effect of the drip characteristics of the uses can contain reinforcing fillers such as mineral polyester during ignition, it has been found that meansilicates, silica obtained by evaporation of a silica sol, ingful values which measure the actual contribution of the quartz, silica gel, glass fibers, cristobalite, asbestos, clay, flame retardant additive can now be obtained. Accordtalc, etc., which improve the heat and shock resistance, ingly, the adopted test was vertical burning test UL746 modulus of elasticity, resistance to creep and other propermodified in the following three respects: ties such as, for example, tensile strength, flexural strength (1) the Size of the test Strip measured 3 inches X 1A inch and hardness. Reinforced polyester compositions for moldx inch mg use preferably contam g about 5 g g g (2) the ignition source was a inch diameter Bunsen most preferably i 3 out to a out y burner adjusted to produce a blue flame approximately weight of the composition of glass in the form of fibers, inch high and Strands or rovings having an average length of at least (3) the flame ontact time with the free end of the test about stri wa 5 seconds In addition to the bromine-containing polyether, the p S composition of the invention can also contain an antimony The invention is further illustrated by the following compound such as antimony trioxide, triphenylstibine, examples wherein all parts and percentages are by weight antimony sulfide, antimony naphthenate or the like a unless otherwise specified. Throughout this specification flame retardant. The presence of an antimony compound the term flame retardant is used to designate a comis not essential to flame retardancy. If present the amount position or article which will meet the requirements of of antimony compound will usually be less than 10% and ASTM D-635 and have a burn time of less than 60 preferably will range from 0.5 to 5% by weight of the seconds determined according to the modified vertical composition. Small amounts of stabilizing agents, lubriburning test UL-746 described above. cants, dye additives, pigments, antistatic agents, nucleat- 4O ing agents, and the like can also be present provided of EXAMPLES 1 To 6 course, that the amount of such additives does not de- In these examples Various molding compositions were tract from ffl YetardmcY Q the compositionmade by intimately blending poly (ethylene terephthalate) composltlons of lnvelltlon can be P a by with the flame retardant(s) in an inline reciprocating 1111x111? the po y Wlth the flame fetardant, the screw injection molding machine using a barrel temperabrommecomalmng Polyether and anmnony compound ture of 285 C. and then compression molding the if present, in conventional manner, e.g. on roll mills, blends into plaques 1/ inch X 3 inch X 3 inches long kneaders or extruders or by agitat ng 1n the presence of an using a 4 000 Press at 235 f 10 i organic solvent. Since uniform mixing of the constituents The plaques were then out into the proper Size ship is essential to reliable results, the mixing operation is f testing The polwethylene terephthalate) used i h preferably carrled out by first dry mixing the ingredients examples was a commercial polflethylene terephthalate) and then subjecting the dry mixture to intensive mechanihaving an intrinsic viscosity of 61 (determined on a Ca} Working at elevated temperatures above ths soften 1% solution in 60/40 phenol/tetrachloroethane at 25 ing point of the polyester and most conveniently by means C.) The brominewomaim-ng polyether was 1 3 0f CQmPOIIHdIIIg s a P 'Y nllxer and (bromomethyl)oxetane] containing 65.6% bromine. The continuing the working until a uniform mixture is obpolyethelhad a ft i point f about and tamed was insolub1e"at'l00 C. in cyclohexanone, toluene and The Pmflltla1 fiammablllty of 11116211 Saturated Pfllyesters a-chloronaphthalene. The antimony trioxide, when pressuch as P l y terephthalate) cannot be meaningent, was in finely divided form and passed a US. Standard fully evaluated according to the standard methods used Si N 2() for most polymers due to the softening and melting-out Details as to the amount of each component in the characteristics of the polyesters. For example, when the compositions and flame retardan'cy test results on the flame retardancy of poly(ethylene terephthalate) is evalumolded bars therefrom are given in the following Table I.

TABLE I Composition (parts by weight) Flame retards-nay rating Poly[3,3bis Poly (ethylene (bromomethyD- Antimony Vertical ASTM terephthalate) oxetano] t-rioxide burn test; D635 Control A 1 0 120 Pass. Example 1 98.4 1.6 120 Do. Example 2 96. 8 3. 2 30 D0. Example 3-- 93.75 6.25 20 Do. Example 4... 90.9 9.1 10 Do. Example 5-- 97.6 1.6 25 Do. Example6 95.2 3.2 5 Do. Control B 99. 2 l Do.

1 Average of 6 tests; results ranged from 60 to greater than 1% seconds.

EXAMPLES 7 TO 12 of glass fibers having an average length of 0.25 inch 5 and a diameter of 0.0005 inch, and 0.1% of talc as a nucleating agent. The compositions were next dried at 130 C. for 16 hours and then molded into plaques according to the procedure of Examples 1 to 6. Flame where R is a bromine substituted methyl group, R is R, chloromethyl, alkoxymethyl or an alkyl group and R and R are hydrogen or an alkyl group, said alkoxy and alkyl groups containing from 1 to 18 carbon atoms.

2. The composition of claim 1 wherein the polyester is poly( ethylene terephthalate) 3. The composition of claim 2 wherein the polyether is a polymer of 3,3-bis(bromomethyl)oxetane.

4. The composition of claim 3 also containing by retardancy test results on the molded bars therefrom Weight from 5 to 60% of a reinforcing finer are given in the following Table II.

TABLE II Composition (parts by weight) Poly Flame retardancy [3,3-blsrating (bromo- Poly (ethylene methyl)- Antimony Vertical ASTM terephthalate) Glass oxetane] trioxlde burn test D635 Control 0......... 67.0 33.0 120 Fall. Example 7 65. 6 32.8 1. 6 120 Pass. Example 8 64. 5 32. 3 3. 2 50 Do. Example 9 65. 0 32. 6 1.6 22 Do Example 1 63. 5 31. 7 3. 2 4 Do. Example 1 62. 5 31.3 6.2 7 Do. Example l 60.6 30.3 6. 1 2 Do. Control D 65. 5 32. 0 120 D0.

What I claim and desire to protect by Letters Patent is: 1. A flame retardant composition comprising a blend of a linear saturated polyester having an average molecular weight of at least about 10,000 and as a flame retardant, based on the weight of the composiiton, 3 to of a bromine-containing polyether when said polyether is the sole flame retardant or 1 to 15% of said polyether combined with 0.5 to 5% of an antimony compound, said polyether having a weight average molecular weight of at least about 700 and a bromine content of at least 48% and being a polymer of 1 R CH Ri 5. The composition of claim 4 wherein the reinforcing 0 filler is glass fibers.

6. The composition of claim 5 wherein the glass fibers are present in the amount of to References Cited UNITED STATES PATENTS 40 LEWIS T. JACOBS, Primary Examiner US. Cl. X.R. 260-860, DIG 24 

